Loop heat pipe and fabrication method therefor, and electronic device

ABSTRACT

A evaporator of a loop heat pipe includes a liquid inlet side portion that extends in a widthwise direction crossing with a lengthwise direction from a liquid inlet side to a vapor outlet side, a plurality of portions that continue to the liquid inlet side portion and extend in the lengthwise direction, a plurality of vapor flow paths that are provided between the plurality of portions and extend in the lengthwise direction, and a vapor outlet side vapor flow path that extends in the widthwise direction and continues to the vapor flow paths. Each of the plurality of portions includes a first groove communicating two adjacent ones of the vapor flow paths.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of InternationalApplication PCT/JP2015/075081 filed on Sep. 3, 2015 and designated theU.S., the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a loop heat pipe and afabrication method therefor, and an electronic device.

BACKGROUND

In a small and thin electronic device for mobile applications such as,for example, a smartphone or a tablet computer, in order to cool aheat-generating component, a sheet-type heat conductive member such as,for example, a metal plate or a thermal diffusion sheet is widely used.For example, though copper, aluminum, magnesium alloy, a stacked thinplate formed from such metals or the like is used as the metal plate,heat conduction of the metal plates is restricted by a physical propertyvalue of their material. Further, however for example, a graphite sheetis used as a thermal diffusion sheet, the thermal conductivity isapproximately 500 to 1500 W/mK, and there is the possibility that such alevel of the thermal conductivity as just described may result infailure to cope with increase of the heat generation of aheat-generating component.

Therefore, in order to efficiently move and diffuse a large amount ofheat, it seems a recommendable idea to utilize a heat pipe that is aheat transfer device which uses latent heat by a vapor-liquid two-phaseflow. For example, for a heat pipe having a diameter of approximately 3to 4 mm, the equivalent thermal conductivity of a heat pipe correspondsto approximately 1500 to 2500 W/mK and exhibits a high heat conductioncompared with that of a sheet-like heat conductive member.

In order to transfer heat efficiently, it is effective to increase thediameter of a pipe, however, this makes an obstacle upon mounting, andapplication to a mobile electronic device does not advance.

In this case, although it seems recommendable to flatten the pipe shapeof the heat pipe, such flattening obstructs the flow of working fluid inthe heat pipe and degrades the performance of heat transport, and theequivalent thermal conductivity of a heat pipe decreases to a level ofapproximately 500 to 1500 W/mK.

In contrast, in a loop heat pipe, flow paths for working fluid of thevapor phase and working fluid of the liquid phase are independent ofeach other and working fluid flows in one direction in the flow paths.Therefore, in comparison with a heat pipe in which working fluid of thevapor phase and working fluid of the liquid phase reciprocate in the onepipe, the flow resistance to the working fluid can be reduced andefficient heat transport can be implemented.

Therefore, it seems recommendable to use a loop heat pipe in anelectronic device for mobile applications.

SUMMARY

According to an aspect of the embodiment, a loop heat pipe includes anevaporator in which working fluid of the liquid phase evaporates, acondenser in which working fluid of the vapor phase condenses, a vaporline that couples the evaporator and the condenser and through which theworking fluid of the vapor phase flows, and a liquid line that couplesthe condenser and the evaporator and through which the working fluid ofthe liquid phase flows, wherein the evaporator includes a liquid inletto which the liquid line is coupled, a vapor outlet to which the vaporline is coupled, a liquid inlet side portion that is provided at theside of the liquid inlet and extends in a widthwise direction crossingwith a lengthwise direction from the side of the liquid inlet to theside of the vapor outlet, a plurality of portions that continue to theliquid inlet side portion and extend in the lengthwise direction, aplurality of vapor flow paths that are provided between the plurality ofportions and extend in the lengthwise direction, and a vapor outlet sidevapor flow path that is provided at the side of the vapor outlet,extends in the widthwise direction and continues to the plurality ofvapor flow paths, each of the plurality of portions includes a firstgroove communicating two adjacent ones of the plurality of vapor flowpaths with each other.

According to an aspect of the embodiment, an electronic device includesa heat-generating component, and a loop heat pipe that cools theheat-generating component, and the loop heat pipe is configured in sucha manner as described above.

According to an aspect of the embodiment, a fabrication method for aloop heat pipe includes processing a region of a first plate-likemember, in which an evaporator is to be formed, to form, in a region inwhich a plurality of portions extending in a lengthwise direction fromthe side of a liquid inlet toward the side of a vapor outlet of theregion serving as the evaporator are to be formed, a first grooveextending in a widthwise direction crossing with the lengthwisedirection and capable of generating capillary force such that, fromamong regions in which a plurality of vapor flow paths are to be formedprovided between the regions in which the plurality of portions are tobe formed, regions in which two vapor flow paths adjacent to each otherare to be formed are communicated with each other, form, in a region inwhich a liquid inlet side portion is to be formed, a third grooveextending in the widthwise direction and capable of generating capillaryforce and form a first wide groove having a width greater than those ofthe first groove and the third groove in the region in which theplurality of vapor flow paths are to be formed and a region in which avapor outlet side vapor flow path is to be formed, processing a regionof a second plate-like member, in which the evaporator is to be formed,to form, in the region in which the plurality of portions are to beformed, a second groove extending in the lengthwise direction andcapable of generating capillary force, form, in a region continuing tothe liquid inlet and a region which each of the plurality of portionscontinues included in the region in which the liquid inlet side portionis to be formed, a fourth groove extending in the lengthwise directionand capable of generating capillary force, and form, in the region inwhich the plurality of vapor flow paths are to be formed and the regionin which the vapor outlet side vapor flow path is to be formed, a secondwide groove having a width greater than those of the second groove andthe fourth groove, and joining the first plate-like member and thesecond plate-like member together such that the side having the firstgroove, third groove and first wide groove and the side having thesecond groove, fourth groove and second wide groove are opposed eachother.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view depicting an example of a configuration of anevaporator provided in a loop heat pipe according to an embodiment;

FIG. 2 is a schematic view depicting a configuration of an electronicdevice that includes the loop heat pipe according to the embodiment;

FIG. 3 is a schematic view depicting a configuration of the electronicdevice that includes the loop heat pipe according to the embodiment;

FIG. 4 is a schematic view illustrating a configuration and operation ofthe loop heat pipe;

FIG. 5 is a schematic view depicting a configuration of a loop heat pipethat uses six thin metal plates;

FIG. 6 is a schematic view illustrating a configuration of flow paths ofa vapor line and a liquid line provided in the loop heat pipe that usessix thin metal plates and a condensation line provided in theevaporator;

FIG. 7 is a schematic view illustrating a configuration of a wickprovided in the inside of the evaporator provided in the loop heat pipethat uses six thin metal plates;

FIG. 8 is a schematic view illustrating movement of working fluid in theinside of the evaporator provided in the loop heat pipe that uses sixthin metal plates;

FIGS. 9A to 9C are views depicting infrared thermography images whenheat is inputted to the evaporator provided in the loop heat pipe thatuses six thin metal plates;

FIG. 10 is a view depicting temperature profiles of different portionsof the loop heat pipe when the loop heat pipe that uses six thin metalplates is started;

FIG. 11 is a view depicting temperature measurement portions of the loopheat pipe when a temperature profile at each portion upon starting ofthe loop heat pipe that uses six thin metal plates is measured;

FIG. 12 is a schematic view depicting an example of a configuration ofthe evaporator provided in the loop heat pipe according to theembodiment;

FIG. 13 is a schematic view depicting an example of a configuration ofthe evaporator provided in the loop heat pipe according to theembodiment;

FIG. 14 is a schematic view depicting an example of a configuration ofthe evaporator provided in the loop heat pipe according to theembodiment;

FIG. 15 is a schematic view depicting an example of a configuration ofthe evaporator provided in the loop heat pipe according to theembodiment;

FIG. 16 is a schematic view depicting an example of a configuration ofthe evaporator provided in the loop heat pipe according to theembodiment;

FIG. 17 is a schematic view depicting an example of a configuration ofthe evaporator provided in the loop heat pipe according to theembodiment;

FIG. 18 is a schematic view depicting an example of a configurationwhere the liquid line provided in the loop heat pipe according to theembodiment includes a groove;

FIG. 19 is a schematic view depicting an example of a configurationwhere the liquid line provided in the loop heat pipe according to theembodiment includes a groove and is a sectional view taken along awidthwise direction of the liquid line;

FIG. 20 is a schematic view depicting the example of a configurationwhere the liquid line provided in the loop heat pipe according to theembodiment includes a groove and is a sectional view taken along alengthwise direction of the liquid line at a position indicated by aline A-A′ of FIG. 19;

FIGS. 21A and 21B are schematic views illustrating a particular exampleof a configuration of the loop heat pipe according to the embodiment anda fabrication method for the loop heat pipe;

FIG. 22 is a schematic view depicting an example of a configurationwhere the liquid line provided in the loop heat pipe according to theembodiment includes a groove;

FIG. 23 is a view depicting a temperature profile at an inlet of thecondenser of the loop heat pipe where the loop heat pipe, in which twothin metal plates are used, according to the embodiment is started;

FIG. 24 is a schematic view depicting an example of a configuration ofthe evaporator provided in the loop heat pipe according to theembodiment; and

FIG. 25 is a schematic view depicting an example of a configuration ofthe evaporator provided in the loop heat pipe according to theembodiment.

DESCRIPTION OF EMBODIMENTS

Incidentally, in order to provide a loop heat pipe in a small and thinelectronic device for mobile applications, the thickness of the loopheat pipe are reduced.

However, it has been found that, if the thickness of the loop heat pipeis reduced, then such a situation occurs that the temperature and thepressure become non-uniform in the evaporator of the loop heat pipe, andas a result, fluid flow of the vapor phase from the evaporator does notbecome uniform and it takes much time to start the operation of the loopheat pipe (namely, heat transfer from the evaporator to the condenser).

Therefore, it is desired to shorten the start-up time for heat transferin the loop heat pipe which is reduced its thickness.

In the following, a loop heat pipe and a fabrication method for the loopheat pipe, and an electronic device according to the present embodimentare described with reference to the drawings.

First, the loop heat pipe according to the present embodiment isdescribed with reference to FIGS. 1 to 25.

The loop heat pipe according to the present embodiment is a thin loopheat pipe that is provided in an electronic device used for small andthin mobile applications such as, for example, a smartphone or a tabletcomputer and transfers heat generated in a heat-generating component(for example, an LSI chip) provided in the electronic device to cool theheat-generating component that is a heat source. It is to be noted thata small and thin electronic device for mobile applications ishereinafter referred to also as mobile device. Further, aheat-generating component is hereinafter referred to also as electroniccomponent or heat-generating device.

As depicted in FIG. 2, the loop heat pipe of the present embodimentincludes an evaporator 2 in which working fluid of the liquid phase isevaporated, a condenser 3 in which working fluid of the vapor phase iscondensed, a vapor line 4 that couples the evaporator 2 and thecondenser 3 to each other and through which working fluid of the vaporphase flows, and a liquid line 5 that couples the condenser 3 and theevaporator 2 to each other and through which working fluid of the liquidphase flows. Here, the condenser 3 includes a condensation line 3A and aheat diffusion plate (heat radiation plate) 3B. As depicted in FIGS. 2and 3, the loop heat pipe 1 configured as described above isaccommodated in the inside of a mobile device 6 such that the evaporator2 is thermally coupled to a heat-generating component 7 provided in themobile device 6. It is to be noted that the working fluid is, forexample, water, ethanol, acetone, methanol, Freon or the like.

Here, the evaporator 2 has one liquid inlet and one vapor outlet, andthe condenser 3 has one vapor inlet and one liquid outlet. The vaporoutlet of the evaporator 2 and the vapor inlet of the condenser 3 arecoupled to each other through the vapor line 4, and the liquid outlet ofthe condenser 3 and the liquid inlet of the evaporator 2 are coupled toeach other through the liquid line 5. In particular, the evaporator 2,vapor line 4, condenser 3, and liquid line 5 are coupled in a loop toeach other, and working fluid sealed in the inside thereof flows in onedirection. Here, the working fluid changes from the liquid phase to thevapor phase by heat supplied from the heat-generating component 7 to theevaporator 2 and moves to the condenser 3 through the vapor line 4together with the heat, and the working fluid changes from the vaporphase to the liquid phase by heat radiation therefrom in the condenser 3and returns to the evaporator 2 through the liquid line 5. Therefore, incomparison with a heat pipe in which working fluid of the liquid phaseand working fluid of the vapor phase move back and forth in the pipe,the flow resistance to the working fluid can be reduced and efficientheat transport can be achieved.

Further, as depicted in FIG. 7, the evaporator 2 includes a liquid inlet8 to which the liquid line 5 is coupled, a vapor outlet 9 to which thevapor line 4 is coupled, a liquid inlet side portion 10 and a pluralityof portions 11 in which the working fluid of the liquid phase permeatesand changes to the vapor phase, and a plurality of vapor flow paths 12and a vapor outlet side vapor flow path 13 through which the workingfluid of the vapor phase flows.

Here, the liquid inlet side portion 10 is a portion that is provided atthe liquid inlet 8 side and extends in the widthwise direction crossingwith a lengthwise direction from the side of the liquid inlet 8 towardthe side of the vapor outlet 9 and in which capillary force is generatedsuch that the working fluid of the liquid phase permeates and changes tothe working fluid of the vapor phase. It is to be noted that thelengthwise direction is hereinafter referred to also as lengthwisedirection of the evaporator 2. Further, the widthwise direction ishereinafter referred to also as widthwise direction of the evaporator 2.Further, since a structure body is provided at the liquid inlet sideportion 10, the structure body is hereinafter referred to also as liquidinlet side structure body.

Further, the plurality of portions 11 are portions that are continuousto the liquid inlet side portion 10 and extend in the lengthwisedirection and in which capillary force is generated and the workingfluid of the liquid phase permeates to change to the working fluid ofthe vapor phase. Here, the plurality of portions 11 are combtooth-shaped portions, namely, a plurality of portions having a combtooth shape. It is to be noted that, since a structure body is providedon the plurality of portions 11, the plurality of portions 11 arehereinafter referred to also as plurality of structure bodies.

Further, the plurality of vapor flow paths 12 are provided between theplurality of portions 11 and extend in the lengthwise direction suchthat the working fluid of the vapor phase flows therealong. Inparticular, the plurality of vapor flow paths 12 and the plurality ofportions 11 are disposed alternately in an in-plane direction, and, as aresult, reduction in thickness of the evaporator 2 is achieved. It is tobe noted that, since the vapor flow paths 12 are flow paths fordischarging the working fluid of the vapor phase flowing in the insideof the evaporator 2 to the vapor line 4 therethrough, the plurality ofvapor flow paths 12 are hereinafter referred to also as vapor flowpaths.

Further, the vapor outlet side vapor flow path 13 is provided at theside of the vapor outlet 9 and extends in the widthwise direction, andcontinues to the plurality of vapor flow paths 12 such that the workingfluid of the vapor phase flows therein.

Especially, as depicted in FIG. 1, each of the plurality of portions 11includes a first groove 14 for communicating two vapor flow pathsadjacent to each other from among the plurality of vapor flow paths 12.Since the vapor flow paths 12 adjacent to each other are communicatedwith each other by the first groove 14 in this manner, a pressuredifference between the vapor flow paths 12 disappears, and the workingfluid of the vapor phase generated by heat from the heat-generatingcomponent 7 that is a heat source is discharged uniformity.Consequently, the start-up time period of the loop heat pipe 1 can bereduced.

In particular, the evaporator 2 may be configured so as to include afirst plate-like member 16 having a first groove 14 and a wide groove 15that has a width greater than that of the first groove 14 and serves aspart of the plurality of vapor flow paths 12 and the vapor outlet sidevapor flow path 13. Here, the first plate-like member 16 is a metalplate and particularly is a copper plate. Further, the first plate-likemember 16 has the first groove 14 and the wide groove 15 provided so asto have a depth smaller than the plate thickness of the plate byprocessing such as, for example, half etching. Here, as the first groove14, a plurality of grooves extending in the widthwise direction areprovided in a juxtaposed relationship in parallel to each other in thelengthwise direction. Further, the first groove 14 here is provided soas to extend in a direction orthogonal to an extending direction of theplurality of vapor flow paths 12 such that the extending direction ofthe plurality of vapor flow paths 12 and the extending direction of thefirst groove 14 cross with each other.

Incidentally, the reason why such a configuration as described above isapplied is such as described below.

As depicted in FIG. 4, the loop heat pipe 1 includes the evaporator 2,condenser 3, and vapor line 4 and liquid line 5 that couple theevaporator 2 and the condenser 3 to each other, and the working fluid issealed with a constant pressure in the inside thereof.

The working fluid changes from the liquid phase to the vapor phase byheat supplied from the heat-generating component 7, and moves to thecondenser 3 through the vapor line 4 together with the heat. The workingfluid changes from the vapor phase to the liquid phase by heat radiationin the condenser 3, and returns to the evaporator 2 through the liquidline 5.

A member (not depicted) called wick having fine holes (pores) isaccommodated in the inside of the evaporator 2, and capillary force isgenerated in the pores when the working fluid permeates into the wickand acts as pumping force for the fluid flow.

If the evaporator 2 is heated by heat generated by the heat-generatingcomponent 7, then the working fluid of the liquid phase permeated in thewick is evaporated on the surface of the wick thereby to generate theworking fluid of the vapor phase. Since the heat generated by theheat-generating component 7 is used for the phase change in theevaporator 2, the heat is deprived of the heat-generating component 7.Then, the working fluid of the vapor phase generated in the evaporator 2moves to the condenser 3 through the vapor line 4 and then changes intothe working fluid of the liquid phase in the condenser 3. By circulationof the working fluid as described above, heat transfer from theheat-generating component 7 is performed successively.

In the loop heat pipe 1, the working fluid of the vapor phase generatedin the evaporator 2 passes through the vapor line 4 and reaches thecondenser 3. At this time, ideally the working fluid of the liquid phaseexists over the flow path from the liquid line 5 side of the condenser 3to the evaporator 2 and the wick in the evaporator 2 is in a state inwhich the working liquid permeates therein. Then, since the capillaryforce in the pores of the wick acts, invasion of the vapor in adirection from the evaporator 2 to the liquid line 5 is suppressed, andthen, the capillary force in the wick acts as a check valve for thevapor.

Incidentally, where such a loop heat pipe 1 as described above isapplied to the mobile device 6 as depicted in FIG. 2, the loop heat pipe1 may be configured from the evaporator 2 contacting with theheat-generating component 7 that is a heat source, vapor line 4,condenser 3 including the condensation line 3A and the heat diffusionplate 3B, and liquid line 5 such that, by transporting heat of theheat-generating component 7 contacting with the evaporator 2 to a regionhaving a comparatively low temperature in the mobile device 6,concentration of heat upon the mobile device can be suppressed.

However, where the loop heat pipe 1 is applied to the mobile device 6,it is desired for the components of the loop heat pipe 1 to have areduced thickness.

For example, if the evaporator 2, vapor line 4, condenser 3 and liquidline 5 that are components of the loop heat pipe 1 are fabricatedseparately from each other and are coupled to each other by brazing orwelding, then it difficult to implement reduction in thickness.

Therefore, it seems recommendable to form a shape of the loop heat pipeby etching process for a plurality of thin metal plates (for example,copper plates) and couple the metal plates by diffusion bonding processto collectively form the evaporator 2, vapor line 4, condenser 3 andliquid line 5 thereby to implement the thin loop heat pipe 1 capable ofbeing accommodated in the mobile device 6.

For example, as depicted in FIG. 5, the thin loop heat pipe 1 can beconfigured by stacking six thin metal plates, namely, two surface sheets17 and 18 and four inner-layer sheets 19 and coupling them by diffusionbonding.

In this case, as depicted in FIG. 6, an opening is provided by etchingin the four inner-layer sheets 19 and the four inner-layer sheets 19having the openings are stacked with the top and the bottom thereofsandwiched by the two surface sheets 17 and 18, respectively. By this,the top and the bottom of the space formed from the openings of the fourinner-layer sheets 19 are closed thereby to form the flow path of thevapor line 4, liquid line 5 and the condensation line 3A provided in thecondenser 3.

Further, as depicted in FIG. 7, the wick 20 that is a structure that isprovided in the inside of the evaporator 2 and generates capillary forcefor fluid driving is formed by providing a plurality of pores having,for example, a diameter of approximately 0.2 mm in each of the fourinner-layer sheets 19 by etching and by displacing the position of thepores provided in each of the inner-layer sheets 19 between the pores inthe inner-layer sheets 19 positioned adjacent to each other in an upwardand downward direction such that at least part of the pores areoverlapped and communicated with each other and fine channels extendthree-dimensionally. By providing such a wick 20 as described above, thecontact area with the working fluid, namely, the evaporation area, canbe increased. It is to be noted that, for details, PCT/JP2013/083504,the entire content of which is incorporated herein by reference, is tobe referred to.

Further, the vapor flow paths 12 for evacuating vapor to the vapor line4 side are provided in the inside of the evaporator 2. Therefore, wherethe thin loop heat pipe 1 is implemented in such a manner as describedabove, it seems recommendable to provide the wick 20 provided in theinside of the evaporator 2 by forming as depicted in FIG. 7. In thiscase, the wick 20 includes a portion (coupling portion) 20A at the sideat which the liquid line 5 of the evaporator 2 is coupled thereto and aplurality of branching portions (rib-like portions) 20B branching fromthe portion 20A. The portion at which the wick 20 in the inside of theevaporator 2 is provided serves as the liquid inlet side portion 10 andthe plurality of portions 11, and the portion at which the wick 20 isnot provided serves as the plurality of vapor flow paths 12 and thevapor outlet side vapor flow path 13. In this manner, where the thinloop heat pipe 1 is implemented in such a manner as described above, inthe inside of the evaporator 2, it seems recommendable to alternatelyarrange the plurality of comb tooth-shaped portions of the wick 20 asthe plurality of portions 11 extending along a direction in which theworking fluid flows and the vapor flow paths 12 as the vapor flow pathextending along the direction in which the working fluid flows along adirection orthogonal to a direction in which the working fluid flows inthe same plane. For example, by configuring the four inner-layer sheets19 so as to have a portion having a plurality of pores that serve as theliquid inlet side portion 10 and the plurality of portions 11 andopenings that function as the vapor flow paths 12 and 13 and stackingand diffusion boding them, the evaporator 2 having the wick 20 and thevapor flow paths 12 and 13 can be formed.

In this case, as depicted in FIG. 8, if the working liquid flowing fromthe liquid line 5 side into the evaporator 2 permeates into the insideof the wick 20 and is evaporated into vapor by heat from the heatsource, then the vapor is evacuated to the vapor line 4 through thevapor flow paths 12 and 13 provided between the plurality of portions 11of the wick 20. It is to be noted that FIG. 8 exemplifies flow of theworking fluid in the evaporator 2 that includes the wick 20 that in turnincludes seven branching portions (comb tooth-like portions) 20B and sixvapor flow paths 12 (in FIG. 8, refer to reference characters (1) to(6)) are provided between the branching portions 20B. Further, in FIG.8, a flow of the working liquid is indicated by a broken line and a flowof vapor is indicated by a solid line.

Here, FIGS. 9A to 9C depict infrared thermography images when heat isapplied to the evaporator 2. It is to be noted that, in FIGS. 9A and 9C,a light color region and a dark color region indicate that thetemperature is high and low, respectively. In actual infraredthermography images, a light color region is a white region and a darkcolor region is a red region. A behavior of the working fluid in theinside of the evaporator 2 can be inferred from a temperaturedistribution in the infrared thermography images.

Here, since a heat source is disposed at a lower portion of theevaporator 2 and the entire evaporator is warmed by heat conduction of athin metal plate (here, a copper plate) configuring the evaporator 2just after applying the hear, from the heat source to the evaporator 2,the evaporator 2 is displayed in a light color (white).

Then, if the working liquid in the evaporator 2 begins to be evaporated,then, as depicted in FIG. 9A, the vapor first flows toward the vaporline 4 in the vapor flow path 12 denoted by reference character (1) inFIG. 9A. Since the heat is deprived at this time, the region of thevapor flow path 12 denoted by reference character (1) in FIG. 9A isplaced into a lower temperature state than that of the surroundings, andthe vapor flow path 12 is displayed in a dark color (red).

Then, as depicted in FIG. 9B, the vapor is evacuated from the vapor flowpath 12 denoted by reference character (3) in FIG. 9B to the vapor line4, and portions of the vapor flow path 12 denoted by referencecharacters (1) and (3) in FIG. 9B are placed into a lower temperaturethan that of the surroundings and the vapor flow path 12 is displayed ina dark color (red).

Then, as depicted in FIG. 9C, the vapor is evacuated from the vapor flowpath 12 denoted by reference character (2) in FIG. 9C, and regions ofthe vapor flow path 12 denoted by reference characters (1), (3) and (2)in FIG. 9C are placed into a lower temperature state than that of thesurroundings and the vapor flow path 12 is displayed in a dark color(red). Thereafter, the vapor is evacuated from the vapor flow path 12denoted by reference character (5) in FIG. 9C, and regions of the vaporflow path 12 denoted by reference characters (1), (3), (2) and (5) inFIG. 9C are placed into a lower temperature state than that of thesurroundings and the vapor flow path 12 is displayed in a dark color(red).

In this manner, if the wick provided in the inside of the evaporator 2is provided in a patterned state as depicted in FIG. 7 in order toimplement the thin loop heat pipe 1 as described above, then dischargeof vapor is performed after time lags in order from the vapor flow path12 denoted by reference character (1) in FIG. 8, vapor flow path 12denoted by reference character (3) in FIG. 8, vapor flow path 12 denotedby reference character (2) in FIG. 8, vapor flow path 12 denoted byreference character (5) in FIG. 8, vapor flow path 12 denoted byreference character (4) in FIG. 8 and vapor flow path 12 denoted byreference character (6) in FIG. 8.

It is considered that the order in vapor evacuation arises from avariation in temperature and pressure in the vapor flow path 12 uponevaporation of the working liquid in the evaporator 2.

Incidentally, when the working liquid in the evaporator 2 is evaporatedby heat from the heat source and the vapor passes through the vapor line4 and then advances to the condenser 3, a temperature rise at thecomponents of the loop heat pipe 1 is observed.

Thus, a period of time after the heat is applied to the evaporator 2until the temperature at the inlet of the condenser 3 rises, namely, theperiod of time after the heat is applied to the evaporator 2 until,after the temperature of the evaporator 2 rises, the heat is transportedand the temperature drops, can be considered the start-up time period ofthe loop heat pipe 1.

Here, FIG. 10 depicts a temperature profile of the components of theloop heat pipe 1 when the loop heat pipe 1 is activated.

In FIG. 10, a solid line A indicates a result when the temperature at alocation denoted by EVP in FIG. 11, namely, the temperature EVP of theevaporator 2 of the loop heat pipe 1, is measured. Further, in FIG. 10,a solid line B indicates a result when the temperature at a locationindicated by EVP-OUT in FIG. 11, namely, the temperature EVP-OUT at theoutlet of the evaporator 2, is measured. Further, in FIG. 10, a solidline C indicates a result when the temperature at a location indicatedby V1 in FIG. 11, namely, the temperature V1 at the evaporator 2 side ofthe vapor line 4, is measured. Further, in FIG. 10, a solid line Dindicates a result when the temperature at a location indicated by V2 inFIG. 11, namely, the temperature V2 at an intermediate portion of thevapor line 4, is measured. Further, in FIG. 10, a solid line E indicatesa result when the temperature at a location indicated by V3 in FIG. 11,namely, the temperature V3 at the condenser 3 side of the vapor line 4,is measured. Further, in FIG. 10, a solid line F indicates a result whenthe temperature at a location indicated by CND-IN in FIG. 11, namely,the temperature CND-IN of the inlet of the condenser 3, is measured.

It has been found that, if the wick 20 provided in the inside of theevaporator 2 is patterned and provided as depicted in FIG. 7 in order toimplement the thin loop heat pipe 1 in such a manner as described above,then since a distribution appears in the temperature and the pressure inthe evaporator 2 and discharge of the vapor becomes non-uniform, thestart-up time period of the loop heat pipe 1 becomes approximately 190seconds as depicted in FIG. 10 and a long period of time is required forstart-up of the loop heat pipe 1 (namely, for heat, transfer from theevaporator 2 to the condenser 3).

Thus, in order to reduce the start-up time period to start heat transferas quickly as possible in the loop heat pipe 1 in which the evaporator 2has a reduced thickness, the evaporator 2 is configured such that, asdescribed hereinabove, the plurality of portions 11 individually includethe first groove 14 for communicating two vapor flow paths 12 adjacentto each other from among the plurality of vapor flow paths 12 asdepicted in FIG. 1.

Since the vapor flow paths 12 adjacent to each other are communicatedwith each other by the first groove 14 in this manner, the pressuredifference between the vapor flow paths 12 disappears and the pressuredistribution in the evaporator 2 upon vapor generation disappears, andthe working fluid of the vapor phase generated by heat from the heatsource is evacuated uniformly to the vapor line 4. Consequently, thestart-up time period of the loop heat pipe 1 can be reduced.

In this case, in the inside of the evaporator 2, in the evaporator 2provided in the thin loop heat pipe 1 described above in which the wick20 patterned as depicted in FIG. 7 is provided, the plurality ofportions 11 individually include the first groove 14 for communicatingvapor flow paths 12 adjacent to each other from among the plurality ofvapor flow paths 12 as depicted in FIG. 1.

In particular, where the six thin metal plates, namely, the two surfacesheets 17 and 18 and the four inner-layer sheet 19, are stacked anddiffusion bonded to configure the thin loop heat pipe 1 as describedhereinabove (refer to FIGS. 5 to 7), as the first groove 14, a pluralityof grooves extending in the widthwise direction may be provided in aparallel and juxtaposed relationship in the lengthwise direction to eachother in the region, in which the plurality of portions 11 of theevaporator 2 of at least one of the two surface sheets 17 and 18 are tobe formed, so as to have a depth smaller than the plate thickness byprocessing such as, for example, half etching, and further, the firstwide groove 15 may be provided in the region, in which the plurality ofvapor flow paths 12 and the vapor outlet side vapor flow path 13 are tobe formed. It is to be noted that the number of thin metal plates, thenumber of first grooves 14 or first wide grooves 15, the distance or theshape are not limited to those exemplified here.

In this case, the evaporator 2 is structured such that the firstplate-like member 16 (here, one of the two surface sheets 17 and 18)having the first groove 14 and the first wide width 15 that has a widthgreater than that of the first groove 14 and is to serve as part of theplurality of vapor flow paths 12 and the vapor outlet side vapor flowpath 13 and the plurality of third plate-like members (here, fourinner-layer sheets 19) having a portion having a plurality of pores andan opening to serve as part of the plurality of vapor flow paths 12 andthe vapor outlet side vapor flow path 13 are joined together. Theplurality of portions 11 and the liquid inlet side portion 10 includethe wick 20 (refer to FIG. 7) configured by stacking the portion havingthe plurality of pores such that at least the part of the pores overlapand are communicated with each other. It is to be noted here that theplurality of third plate-like members are metal plates (thin metalplates), and particularly are copper plates (thin copper plate).

Incidentally, where the plurality of portions 11 include the firstgroove 14 as described above, the first groove 14 may be configured as agroove capable or generating capillary force. In this case, as depictedin FIG. 12, it is preferable to configure each of the plurality ofportions 11 so as to have a second groove 21 extending in the lengthdirection and configure the second groove 21 also as a groove capable ofgenerating capillary force. By providing such a second groove 21 as justdescribed, it is possible to allow the working fluid of the liquid phaseto flow toward the lengthwise direction. In particular, if the firstgroove 14 described above and capable of generating capillary force isprovided, then the working fluid of the liquid phase becomes likely tospread toward the widthwise direction but becomes less likely to flowtoward the lengthwise direction. Therefore, by providing the secondgroove 21 capable of generating capillary force, the working fluid ofthe liquid phase is permitted to be likely to flow toward the lengthwisedirection.

In this case, the evaporator 2 may be configured such that it includesnot only the first plate-like member 16 described hereinabove (refer toFIG. 1; one of the surface sheets 17 and 18 of FIG. 5) and she thirdplate-like members (four inner-layer sheets 19 of FIG. 5) but also asecond plate-like member 23 having the second groove 21 and a secondwide groove 22 that has a width greater than that of the second groove21 and is to serve as part of the plurality of vapor flow paths 12 andthe vapor outlet side vapor flow path 13, and the first groove 14 andthe second groove 21 are configured individually as grooves capable ofgenerating capillary force. Here, the second plate-like member 23 is ametal plate (thin metal plate) and particularly is a copper plate (thincopper plate). Further, the second plate-like member 23 includes thesecond groove 21 and the second wide groove 22 provided so as to have adepth smaller than the plate thickness by processing such as, forexample, half etching. Here, as the second groove 21, a plurality ofgroove extending in the length direction are provided in a parallel andjuxtaposed relationship to each other in the widthwise direction.Further, the first groove 14 and the second groove 21 are provided so asto be orthogonal to each other. It is to be noted that the number, thedistance and the shape of the second grooves 21 and second wide grooves22 are not limited to those exemplified here.

In particular, where the six thin metal plates, namely, the two surfacesheets 17 and 18 and the four inner-layer sheets 19, are stacked anddiffusion bonded to configure the thin loop heat pipe 1 as describedhereinabove (refer to FIGS. 5 to 7), such a configuration as describedbelow may be applied. In particular, as depicted in FIG. 1, as the firstgroove 14, a plurality of grooves extending in the widthwise directionand capable of generating capillary force are provided in a parallel andjuxtaposed relationship with each other in the lengthwise direction in aregion, in which the plurality of portions 11 of the evaporator 2 are tobe formed, of one of the two surface sheets 17 and 18 (here, the firstplate-like member 16) so as to have a depth smaller than the platethickness by processing such as, for example, half etching and the firstwide groove 15 is further provided in a region in which the plurality ofvapor flow paths 12 and the vapor outlet side vapor flow path 13 are tobe formed. Further, as depicted in FIG. 12, as the second groove 21, aplurality of grooves extending in the lengthwise direction and capableof generating capillary force are provided in a parallel and juxtaposedrelationship with each other in the widthwise direction in the region,in which the plurality of portions 11 of the evaporator 2 are to beformed, of the other one of the two surface sheets 17 and 18 (here, thesecond plate-like member 23) so as to have a depth smaller than theplate thickness by processing such as, for example, half etching and thesecond wide groove 22 is provided in the region in which the pluralityof vapor flow paths 12 and the vapor outlet side vapor flow path 13 areto be formed.

Incidentally, while the liquid inlet side portion 10 and the pluralityof portions 11 of the evaporator 2 here are configured including thewick 20 (refer to FIG. 7) configured in such a manner as describedabove, the configuration not limited to this, and the liquid inlet sideportion 10 and the plurality of portions 11 of the evaporator 2 may beany portions if they serve as portions at which capillary force isgenerated and working fluid of the liquid phase permeates and changesinto working fluid of the vapor phase. For example, the liquid inletside portion 10 and the plurality of portions 11 of the evaporator 2 maybe configured as portions that do not include the wick 20 configured insuch a manner as described above.

In this case, as depicted in FIGS. 13 and 14, each of the plurality ofportions 11 of the evaporator 2 may be configured including the firstgroove 14 for communicating two vapor flow paths 12 adjacent to eachother from among the plurality of vapor flow paths 12 and the secondgroove 21 extending in the lengthwise direction, and the liquid inletside portion 10 of the evaporator 2 may be configured including thethird groove 24 extending in the widthwise direction and the fourthgroove 25 provided in a region continuing to the liquid inlet 8 and aregion which each of the plurality of portions 11 continues andextending in the lengthwise direction. Further, the first groove 14,second groove 21, third groove 24 and fourth groove 25 may be configuredas grooves capable of generating capillary force. It is to be noted thatthe number, distance and shape of the third groove 24 and the fourthgroove 25 are not limited to those exemplified here.

In this case, not only the first groove 14 and the first wide groove 15but also the third groove 24 may be provided on the first plate-likemember 16 described hereinabove as depicted in FIG. 13. In particular,the first plate-like member 16 described above may be configuredincluding the first groove 14, first wide groove 15 and third groove 24provided so as to have a depth smaller than the plate thickness byprocessing such as, for example, half etching. Here, as the third groove24, a plurality of grooves extending in the widthwise direction areprovided in a parallel and juxtaposed relationship with each other inthe lengthwise direction. Further, the first groove 14 and third groove24 and the portion extending in the lengthwise direction of the firstwide groove 15 (portion in which part of the plurality of vapor flowpaths 12 are to be formed) are provided on the first plate-like member16 here such that the directions in which they extend are orthogonal toeach other. Further, the first groove and third groove 24 and theportion extending in the widthwise direction of the first wide groove 15(portion that is to become part of the vapor outlet side vapor flow path13) are provided on the first plate-like member 16 here such that thedirections in which they extend become parallel to each other.

Or, not only the second groove 21 and second wide groove 22 but also thefourth groove 25 may be provided on the second plate-like member 23described hereinabove as depicted in FIG. 14. In particular, the secondplate-like member 23 described above may be configured including thesecond groove 21, second wide groove 22 and fourth groove 25 provided soas to have a depth smaller than the plate thickness by processing suchas, for example, half etching. Here, as the fourth groove 25, aplurality of grooves extending in the lengthwise direction are providedin a parallel and juxtaposed relationship to each other in the widthwisedirection in the region continuing to the liquid inlet 8 and the regionin which each of the plurality of portions 11 continues. Further, thesecond groove 21 and fourth groove 25 and the portion extending in thelengthwise direction of the second wide groove 22 (portion to becomepart of the plurality of vapor flow paths 12) are provided on the secondplate-like member 23 here such that the directions in which they extendare parallel to each other. In particular, on the second plate-likemember 23 here, the plurality of second grooves 21 and fourth grooves 25and the portion extending in the lengthwise direction of the second widegroove 22 (portion that is to become part of the plurality of vapor flowpaths 12) are provided alternately along the widthwise direction.Further, on the second plate-like member 23 here, the second groove 21and fourth groove 25 and the portion extending in the widthwisedirection of the second wide groove 22 (portion that is to become partof the vapor outlet side vapor flow path 13) are provided such that thedirections in which they extend are orthogonal to each other.

It is to be noted here that, since the first groove 14, second groove21, third groove 24 and fourth groove 25 are fine pitch groovesindividually having a size with which capillary force can be generated,the grooves are hereinafter referred to also as fine pitch grooves. Onthe other hand, the first wide groove 15 and the second wide groove 22may be grooves individually having a size capable of configuring a flowpath in which working fluid of the vapor phase flows and is evacuated tothe vapor line 4, and are hereinafter referred to also as grooves.

Further, while grooves 26 and 27 are provided in a region, in which theinlet of the evaporator 2, namely, the liquid inlet 8, is to beprovided, of the first plate-like member 16 and second plate-like member23 here as depicted in FIGS. 13 and 14, the grooves may not be provided,for example, as depicted in FIGS. 15 and 16. Further, while theplurality of grooves 26 extending in the widthwise direction areprovided in a region, in which the inlet of the evaporator 2, namely,the liquid inlet 8, is to be formed, of the first plate-like member 16here as depicted in FIG. 13, the configuration is not limited to this,and a plurality of grooves 28 extending in the lengthwise direction maybe provided, for example, as depicted in FIG. 17.

Further, the evaporator 2 may be structured such that the firstplate-like member 16 including the first groove 14, third groove 24 andfirst wide groove 15 that has a width greater than that of the first andthird grooves 14 and 24 and is to form part of the plurality of vaporflow paths 12 and the vapor outlet side vapor flow path 13 and thesecond plate-like member 23 including the second groove 21, fourthgroove 25 and second wide groove 22 that has a width greater than thatof the second groove 21 and fourth groove 25 and is to form part of theplurality of vapor flow paths 12 and the vapor outlet side vapor flowpath 13 are coupled to each other such that the side having the firstgroove 14, third groove 24 and first wide groove 15 and the side havingthe second groove 21, fourth groove 25 and second wide groove 22 areopposed to each other. By configuring the evaporator 2 from the twoplate-like members of the first plate-like member 16 and the secondplate-like member 23 in this manner, the cost can be reduced. In short,reduction in thickness, reduction of the start-up time period andreduction of the cost of the loop heat pipe 1 can be implemented.

In this case, in the plurality of portions 11 of the evaporator 2, thefirst groove 14 capable of generating capillary force and the secondgroove 21 capable of generating capillary force are provided so as tocross (here, orthogonally) with each other and are communicated witheach other to configure a fine channel. Further, in the liquid inletside portion 10 of the evaporator 2, the third groove 24 capable ofgenerating capillary force and the fourth groove 25 capable ofgenerating capillary force axe provided so as to cross (here,orthogonally) with each other and are communicated with each other toconfigure a fine channel.

Consequently, in the liquid inlet side portion 10 and the plurality ofportions 11 of the evaporator 2, the grooves 14, 24, 21 and 25 providedat the portions function similarly to a wick provided in the inside ofan evaporator of a general loop heat pipe so as to generate capillaryforce such that working fluid of the liquid phase permeates and ischanged into working fluid of the vapor phase.

Especially, the second groove 21 and the fourth groove 25 extend in thelengthwise direction of the evaporator 2, namely, in the direction inwhich working fluid of the liquid phase flows. Therefore, if workingfluid of the liquid phase flowing into the evaporator 2 from the liquidline 5 flows into the second groove 21 and the fourth groove 25, thencapillary force is generated and, by the capillary force, the workingfluid flows toward the side to which the vapor line 4 is coupled alongthe lengthwise direction of the evaporator 2. Further, the first groove14 and the third groove 24 extend along the widthwise direction of theevaporator 2. Therefore, if the working fluid of the liquid phaseflowing into the evaporator 2 from the liquid line 5 flows into thefirst groove 14 and the third groove 24, then capillary force isgenerated and, by the capillary force, pumping force is generated in thewidthwise direction of the evaporator 2 and causes the working fluid toflow along the widthwise direction of the evaporator 2. In this manner,the working fluid of the liquid phase is caused to flow so as to spreadin a planar direction by the first groove 14, second groove 21, thirdgroove 24 and fourth groove 25. Further, since the two vapor flow paths12 adjacent to each other from among the plurality of vapor flow paths12 are communicated with each other by the first groove 14, the pressuredifference between the plurality of vapor flow paths 12 disappears andthe working fluid of the vapor phase is evacuated uniformly, and thestart-up time period of the loop heat pipe 1 can be reduced.

Further, the plurality of vapor flow paths 12 of the evaporator 2 areconfigured from the portion of the first wide groove 15 extending in thelengthwise direction and the portion of the second wide groove 22extending in the lengthwise direction. Further, the vapor outlet sidevapor flow path 13 of the evaporator 2 is configured from the portion ofthe first wide groove 15 extending in the widthwise direction and theportion of the second wide groove 22 extending in the widthwisedirection.

In particular, the thin loop heat pipe 1 may be configured in thefollowing manner. The first groove 14, first wide groove 15 and thirdgroove 24 are provided in a region, which is to serve as the evaporator2, of at least one of the two thin metal plates (the two surface sheets)as the first plate-like member 16 and the second plate-like member 23 soas to have a depth smaller than the plate thickness by processing suchas, for example, half etching. Further, the second groove 21, secondwide width 22 and fourth groove 25 are provided in a region, which is toserve as the evaporator 2, of the other one of the two thin metal platesso as to have a depth smaller than the plate thickness by processingsuch as, for example, half etching. Further, concave portions forconfiguring the flow paths of the vapor line 4, condensation line 3Aprovided in the condenser 3 and liquid line 5 are provided in a region,which is to serve as the vapor line 4, a region, which is to serve asthe condensation line 3A provided in the condenser 3, and a region,which is to serve as the liquid line 5, of the two thin metal plates.Then, the two thin metal plates are opposed to each other such that thefaces thereof on which the grooves and concave portions are providedcontact with each other, and are joined together by diffusion bonding.

In this case, by coupling the two plate-like members of the firstplate-like member 16 and the second plate-like member 23, the evaporator2, vapor line 4, condenser 3 and liquid line 5 are integrally formed. Inparticular, the evaporator 2, vapor line 4, condenser 3 and liquid line5 are configured from a same material (here, copper).

Here, the concave port ions provided in the regions, which are to serveas the condensation line 3A, of the first plate-like member 16 and thesecond plate-like member 23 are provided in a meandering pattern suchthat the efficiency in heat exchange with the outside air is raised andliquefaction by condensation can be performed sufficiently. Further,upon patterning into the shape of the evaporator 2, vapor line 4,condenser 3 and liquid line 5, by leaving the plate-like member in theform of a plate around the region, in which the condensation line 3Aprovided in the condenser 3 is to be formed, the portion functions asthe heat diffusion plate 3B provided in the condenser 3.

The loop heat pipe 1 configured from the two plate-like members of thefirst plate-like member 16 and second plate-like member 23 as describedabove can be fabricated in the following manner.

First, a region of the first plate-like member 16, in which theevaporator 2 is to be formed, is half etched to form, in a region inwhich the plurality of portions 11 extending in the lengthwise directionfrom the side of the liquid inlet 8 toward the side of the vapor outlet9 of the region serving as the evaporator 2 are to be formed, a firstgroove 14 extending in the widthwise direction crossing with thelengthwise direction and capable of generating capillary force suchthat, from among regions in which the plurality of vapor flow paths 12provided between the regions in which the plurality of portions 11 areto be provided are to be formed, regions in which two vapor flow paths12 adjacent to each other are to be formed are communicated with eachother, form a third groove 24 extending in the widthwise direction andcapable of generating capillary force in a region in which the liquidinlet side portion 10 is to be formed and form a first wide groove 15having a width greater than those of the first groove 14 and the thirdgroove 24 in a region in which the plurality of vapor flow paths 12 areto be formed and a region in which the vapor outlet side vapor flow path13 is to be formed (for example, refer to FIGS. 13, 15 and 17).

Further, a region of the second plate-like member 23, in which theevaporator 2 is to be formed, is half etched to form a second groove 21extending in the lengthwise direction and capable of generatingcapillary force in a region in which the plurality of portions 11 are tobe formed, form, in a region continuing to the liquid inlet 8 includedin the region in which the liquid inlet side portion 10 is to be formedand a region in which each of the plurality of portions 11 continues, afourth groove 25 extending in the lengthwise direction and capable ofgenerating capillary force and form, in a region in which the pluralityof vapor flow paths 12 are to be formed and a region in which the vaporoutlet side vapor flow path 13 is to be formed, a second wide groove 22having a width greater than those of the second groove 21 and the fourthgroove 25 (for example, refer to FIGS. 14 and 16).

Then, the first plate-like member 16 and the second plate-like member 23are joined together such that the side having the first groove 14, thirdgroove 24 and first wide groove 15 and the side having the second groove21, fourth groove 25 and second wide groove 22 are opposed to eachother.

The loop heat pipe 1 can be fabricated in this manner.

It is to be noted that, while a groove is not provided on any of thevapor line 4, condensation line 3A and liquid line 5 in the loop heatpipe 1 described above, the configuration is not limited to this.

For example, as depicted in FIGS. 18 to 20, the liquid line 5 may beconfigured including a liquid line groove 29 capable of generatingcapillary force.

For example, as depicted in FIG. 18, a liquid line groove 29A extendingin the lengthwise direction of the liquid line 5 and capable ofgenerating capillary force may be provided on the liquid line 5.

In this case, the liquid line 5 may be structured such that a firstliquid line groove 29A extending in the lengthwise direction of a regionin which the liquid line 5 is to be formed and capable of generatingcapillary force is provided in a region of the first plate-like member16 in which the liquid line 5 is to be formed and a second liquid linegroove 29A extending in the lengthwise direction of the region in whichthe liquid line 5 is to be formed and capable of generating capillaryforce is provided in the region of the second plate-like member 23 inwhich the liquid line 5 is to be formed, and the first plate-like member16 and the second plate-like member 23 are joined together such that theside having the first liquid line groove 29A and the side having thesecond liquid line groove 29A are opposed to each other.

Or, in a step of half etching the first plate-like member 16 in thefabrication method for a loop heat pipe described above, a region of thefirst plate-like member 16, in which the liquid line 5 is to be formed,is half etched to form a first liquid line groove 29A extending in thelengthwise direction of the region in which the liquid line 5 is to beformed and capable of generating capillary force, and, in a step of halfetching the second plate-like member 23, a region of the secondplate-like member 23, in which the liquid line 5 is to be formed, ishalf etched to form a second liquid line groove 29A extending in thelengthwise direction of the region in which the liquid line 5 is to beformed and capable of generating capillary force, whereafter, in a stepof joining the first plate-like member 16 and the second plate-likemember 23 together, the first plate-like member 16 and the secondplate-like member 23 are joined together such that the side having thefirst groove 14, third groove 24, first wide groove 15 and first liquidline groove 29A and the side having the second groove 21, fourth groove25, second wide groove 22 and second liquid line groove 29A are opposedto each other.

Further, the liquid line 5 may be configured including the first liquidline groove 29A extending in the lengthwise direction of the liquid line5 and capable of generating capillary force and the second liquid linegroove 29A extending in the widthwise direction of the liquid line 5 andcapable of generating capillary force, for example, as depicted in FIGS.19 and 20.

In this case, the liquid line 5 may be structured such that the firstliquid line groove 29A extending in the lengthwise direction of theregion in which the liquid line 5 is to be formed and capable ofgenerating capillary force is provided in the region of the firstplate-like member 16 in which the liquid line 5 is to be formed asdepicted in FIG. 19 and the second liquid line groove 29B extending inthe widthwise direction of the region in which the liquid line 5 is tobe formed and capable of generating capillary force is provided in aregion of the second plate-like member 23 in which the liquid line 5 isto be formed, and the first plate-like member 16 and the secondplate-like member 23 are joined together such that the side having thefirst liquid line groove 29A and the side having the second liquid linegroove 29B are opposed to each other.

Or, in the step of half etching the first plate-like member 16 in thefabrication method for a loop heat pipe described above, a first liquidline groove 29A extending in the lengthwise direction of a region inwhich the liquid line 5 is to be formed and capable of generatingcapillary force is formed by half etching a region of the firstplate-like member 16 in which the liquid line 5 is to be formed and, inthe step for half etching the second plate-like member 23, a secondliquid line groove 29B extending in the widthwise direction of theregion in which the liquid line 5 is to be formed and capable ofgenerating capillary force is formed by half etching a region of thesecond plate-like member 23 in which the liquid line 5 is to be formed.Then, in the step of joining the first plate-like member 16 and thesecond plate-like member 23 together, the first plate-like member 16 andthe second plate-like member 23 are joined together such that the sidehaving the first groove 14, third groove 24, first wide groove 15 andfirst liquid line groove 29A and the side having the second groove 21,fourth groove 25, second wide groove 22 and second liquid line groove29B are opposed to each other.

Further, for example, the liquid line 5 may be configured including awick in place of the liquid line groove 29. In this case, a wick havinga configuration similar to that of the wick 20 provided in theevaporator 2 described above may be provided also on the liquid line 5.

It is to be noted that the liquid line groove 29 or the wick may beprovided over the overall liquid line 5 or may be provided at part ofthe liquid line 5. Further, the number, distance and shape of the liquidline grooves 29 are not limited to those exemplified here.

The reason why a liquid line groove 29 or a wick capable of generatingcapillary force is provided also on the liquid line 5 as described aboveis that, although a mobile device is sometimes placed in a verticalorientation in which the position of the heat-generating component 7that is a heat source is positioned at the upper side, also in such acase as just described, capillary force acts such that working fluid ofthe liquid phase flows in a part of the liquid line 5 and flows into theevaporator 2 thereby to allow the loop heat pipe 1 to operate instability.

In the following, a particular example of a configuration and afabrication method of the same are described below.

First, one thin copper plate having a thickness of approximately 3 mm isused and patterned with resist and etched such that such a shape asdepicted in FIG. 21A is obtained. Here, the width of the vapor line 4and the condensation line 3A provided on the condenser 3 isapproximately 8 mm, and the width of the liquid line 5 is approximately6 mm. Further, the flow paths of the vapor line 4, condensation line 3Aand liquid line 5 are formed by performing half etching of a thin copperplate to the depth of approximately 0.15 mm. Further, the inside of theevaporator 2 is formed by half etching such that such a pattern asdepicted in FIG. 21A is formed. Here, the width and the depth of thefine grooves that are the first groove 14 and the third groove 24 (forexample, refer to FIGS. 13, 15 and 17) are approximately 0.1 mm andapproximately 0.12 mm, respectively. Further, the width and the depth ofthe groove that is the first wide groove 15 (for example, refer to FIGS.13, 15 and 17) are approximately 1 mm and approximately 0.15 mm,respectively. It is to be noted that, in FIG. 21A, a pattern is appliedto the regions in which the first groove 14 and the third groove 24 areto be provided.

Then, one thin copper plate having a thickness of approximately 3 mm ispatterned with resist and etched such that such a shape as depicted inFIG. 21B is obtained. Here, the thin copper plate processed to such ashape as depicted in FIG. 21A is processed such that the evaporator 2,vapor line 4, condenser 3 and liquid line 5 are disposed at symmetricpositions. Here, the width of the vapor line 4 and the condensation line3A provided on the condenser 3 is approximately 8 mm and the width ofthe liquid line 5 is approximately 6 mm. Further, the flow paths of thevapor line 4, condensation line 3A and liquid line 5 are formed by halfetching the thin copper plate to a depth of approximately 0.15 mm.Further, the inside of the evaporator 2 is formed by half etching suchthat such a pattern as depicted in FIG. 21B is formed. Here, the widthand the depth of the fine grooves that are the second groove 21 and thefourth groove 25 (for example, refer to FIGS. 14 and 16) areapproximately 0.1 mm and approximately 0.12 mm, respectively. Further,the width and the depth of the groove that is the second wide groove 22(for example, refer to FIGS. 14 and 16) are approximately 1 mm andapproximately 0.15 mm, respectively. It is to be noted in FIG. 21B, apattern is applied to the regions in which the second groove 21 and thefourth groove 25 are to be provided.

Then, the loop heat pipe 1 can be produced by diffusion bonding the thincopper plate processed in such a manner as depicted in FIG. 21A and thethin copper plate processed in such a manner as depicted in FIG. 21B,pumping the inside into vacuum through a liquid inlet and then injectingwater (or ethanol or Freon) into the pipe.

It is to be noted that, in order to form a liquid line groove 29 capableof generating capillary force also in the inside of the liquid line 5 asdepicted in FIG. 22 in the loop heat pipe 1 fabricated in such a manneras described above, the liquid line groove 29 may be formed by halfetching in the region of each thin copper plate in which the liquid line5 is to be formed. In this case, the liquid line groove 29A extending inthe lengthwise direction of the liquid line 5 may be formed in theregion of both of the thin copper plates in which the liquid line 5 isto be formed, or the liquid line groove 29A extending in the lengthwisedirection of the liquid line 5 may be formed in the region of one of thethin copper plates in which the liquid line 5 is to be formed while theliquid line groove 29B extending in the widthwise direction of theliquid line 5 is formed in the region of the other thin copper plate inwhich the liquid line 5 is to be formed. Here, the width and the depthof the liquid line grooves 29 may be set to approximately 0.1 mm andapproximately 0.12 mm, respectively. It is to be noted that, in FIG. 22,a pattern is applied to regions in which the first groove 14 and thethird groove 24 are to be provided and a region in which the liquid linegroove 29 is to be provided.

Further, the shape and the piping layout of the loop heat pipe 1 are notlimited to those described above. Further, while a thin copper plate isused as the thin metal plate here, the thin metal plates may be formedcollectively by diffusion bonding. Further, the material of any thinmetal plate is not limited to copper, and a material for patternformation by etching or the like and diffusion bonding may be used.Further, the dimensions of the loop heat pipe 1 are not limited to thosedescribed above and may be optimized suitably in accordance with arequired heat transport amount and a required heat transfer distance, apiping height and a piping width.

Since, in the loop heat pipe 1 produced in such a manner as describedabove, the vapor flow paths 12 adjacent to each other from among theplurality of vapor flow paths 12 are communicated with each other by afine groove that is the first groove 14, the pressure distribution inthe evaporator 2 upon vapor generation disappears and working fluid ofthe vapor phase is evacuated uniformly to the vapor line 4, and, as aresult, the start-up time period of the loop heat pipe 1 can be reduced.

Here, FIG. 23 depicts profiles of an inlet temperature of the condenser3 upon start-up of the loop heat pipe 1 of the embodiment describedhereinabove and a comparative example.

Here, in FIG. 23, a solid line A indicates a profile of the inlettemperature of the condenser 3 of the loop heat pipe 1 of the embodimentdescribed above, namely, of the loop heat pipe 1 that is configured fromtwo thin metal plates in such a manner as described above and in whichthe first groove 14, second groove 21, third groove 24 and fourth groove25 are provided in the evaporator 2. Further, in FIG. 23, a solid line Bindicates a profile of the inlet temperature of the condenser of theloop heat pipe of the comparative example, namely, the loop heat pipethat is configured from six thin metal plates and in which the wick isprovided in the evaporator while the first groove, second groove, thirdgroove and fourth groove are not provided.

As depicted in FIG. 23, while, in the loop heat pipe of the comparativeexample, the time period after heat is applied to the evaporator untilthe temperature of the inlet of the condenser rises is approximately 190seconds, in the loop heat pipe 1 or the embodiment described above, thetime period is reduced to approximately 120 seconds. In this manner,with the loop heat pipe 1 of the embodiment described hereinabove, thestart-up time period can be reduced in comparison with that of the loopheat pipe of the comparative example. By reducing the start-up timeperiod of the loop heat pipe 1 in this manner, the heat of an LSI chip(heat-generating component) that is a heat source such as, for example,a CPU can be transferred in a short period of time, and this provides aneffect that thermal runaway arising from a sudden rise of thetemperature of the LSI is suppressed and function restriction of the LSIchip for suppressing an excessive increase of the temperature isdelayed. As a result, an operation and a use sense comfortable to theuser of the mobile device 6 can be implemented.

Accordingly, with the loop heat pipe and the fabrication method for theloop heat pipe, and the electronic device according to the embodiment,there is an advantage that the start-up time period for heat transfercan be reduced in the loop heat pipe 1 in which the evaporator 2 isreduced in thickness.

It is to be noted that, while, in the embodiment described above, thefirst groove 14 is provided such that it extends in a directionorthogonal to the direction in which the plurality of vapor flow paths12 extend and the direction in which the plurality of vapor flow paths12 extend and the direction in which the first groove 14 extends crosswith each other (for example, refer to FIG. 13), the configuration isnot limited to this, and the first groove 14 may be provided such thatit communicates two vapor flow paths 12 adjacent to each other fromamong the plurality of vapor flow paths 12. For example, as depicted inFIG. 24, the first groove 14 may be provided such that it extends in anoblique direction with respect to the direction in which the pluralityof vapor flow paths 12 extend and the direction in which the pluralityof vapor flow paths 12 extend and the direction in which the firstgroove 14 extends cross with each other.

Further, while, in the embodiment described above, as the first grooveprovided individually at the plurality of portions 11, the plurality ofgrooves 14 extending in the widthwise direction are provided in aparallel and juxtaposed relationship with each other in the lengthwisedirection (for example, refer to FIG. 13), the plurality of grooves 14may not necessarily be provided over the overall length in thelengthwise direction, and, for example, a plurality of grooves 14Xextending in the lengthwise direction may be provided in a parallel andjuxtaposed relationship to each other in the widthwise direction at partin the lengthwise direction as depicted in FIG. 25. In particular, theplurality of grooves 14 extending in the widthwise direction and theplurality of grooves 14X extending in the lengthwise direct ion may beprovided as the first grooves provided individually at the plurality ofportions 11. Here, the plurality of grooves 14 extending in thewidthwise direction and the plurality of grooves 14X extending in thelengthwise direction are provided so as to be orthogonal to each other.

All examples and conditional language provided herein are intended forthe pedagogical purposes of aiding the reader in understanding theinvention and the concepts contributed by the inventor to further theart, and are not to be construed as limitations to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although one or more embodiments of thepresent invention have been described in detail, it should be understoodthat the various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

1-11. (canceled)
 12. A fabrication method for a loop heat pipe,comprising: processing a region of a first plate-like member, in whichan evaporator is to be formed, to form, in a region in which a pluralityof portions extending in a lengthwise direction from the side of aliquid inlet toward the side of a vapor outlet of the region serving asthe evaporator are to be formed, a first groove extending in a widthwisedirection crossing with the lengthwise direction and capable ofgenerating capillary force such that, from among regions in which aplurality of vapor flow paths are to be formed provided between theregions in which the plurality of portions are to be formed, regions inwhich two vapor flow paths adjacent to each other are to be formed arecommunicated with each other, form, in a region in which a liquid inletside portion is to be formed, a third groove extending in the widthwisedirection and capable of generating capillary force and form a firstwide groove having a width greater than those of the first groove andthe third groove in the region in which the plurality of vapor flowpaths are to be formed and a region in which a vapor outlet side vaporflow path is to be formed; processing a region of a second plate-likemember, in which the evaporator is to be formed, to form, in the regionin which the plurality of portions are to be formed, a second grooveextending in the lengthwise direction and capable of generatingcapillary force, form, in a region continuing to the liquid inlet and aregion which each of the plurality of portions continues included in theregion in which the liquid inlet side portion is to be formed, a fourthgroove extending in the lengthwise direction and capable of generatingcapillary force, and form, in the region in which the plurality of vaporflow paths are to be formed and the region in which the vapor outletside vapor flow path is to be formed, a second wide groove having awidth greater than those of the second groove and the fourth groove; andjoining the first plate-like member and the second plate-like membertogether such that the side having the first groove, third groove andfirst wide groove and the side having the second groove, fourth grooveand second wide groove are opposed each other.
 13. The fabricationmethod for a loop heat pipe according to claim 12, wherein, in theprocessing the first plate-like member, an etching process is performedfor the region of the first plate-like member, in which a liquid line isto be formed, to form a first liquid line groove extending in alengthwise direction of the region in which the liquid line is to beformed and capable of generating capillary force; in the processing thesecond plate-like member, an etching process is performed for the regionof the second plate-like member, in which the liquid line is to beformed, to form a second liquid line groove extending in a lengthwisedirection of the region in which the liquid line is to be formed andcapable of generating capillary force; and in the joining the firstplate-like member and the second plate-like member together, the firstplate-like member and the second plate-like member are joined togethersuch that the side having the first groove, third groove, first widegroove and first liquid line groove and the side having the secondgroove, fourth groove, second wide groove and second liquid line grooveare opposed to each other.
 14. The fabrication method for a loop heatpipe according to claim 12, wherein, in the processing the firstplate-like member, an etching process is performed for the region of thefirst plate-like member, in which a liquid line is to be formed, to forma first liquid line groove extending in a lengthwise direction of theregion in which the liquid line is to be formed and capable ofgenerating capillary force; in the processing the second plate-likemember, an etching process is performed for the region of the secondplate-like member, in which the liquid line is to be formed, to form asecond liquid line groove extending in a widthwise direction of theregion in which the liquid line is to be formed and capable ofgenerating capillary force; and in the joining the first plate-likemember and the second plate-like member together, the first plate-likemember and the second plate-like member are joined together such thatthe side having the first groove, third groove, first wide groove andfirst liquid line groove and the side having the second groove, fourthgroove, second wide groove and second liquid line groove are opposed toeach other.